1. Field of the Invention
This invention relates generally to the field of Internet protocol (IP) routing.
2. Description of Related Art
IP routing denotes the set of protocols that determine the path that data follows in order to travel across multiple networks from its source to its destination. Data is routed from its source to its destination through a series of routers, and across multiple networks. The IP routing protocols enable routers to build up a forwarding table that correlates final destinations with next hop addresses.
When an IP packet is to be forwarded, a router uses its forwarding table to determine the next hop for the packet's destination, based on the destination IP address in the IP packet header, and forwards the packet appropriately. The next router then repeats this process using its own forwarding table. This process is repeated until the packet reaches its destination. At each stage, the IP address in the packet header is sufficient information to determine the next hop. No additional protocol headers are required.
In computing and especially computer networks, a lag is a symptom where result of an action appears later than expected. While different kinds of latency are well defined technical terms, lag is the symptom, not the cause.
Latency is the time taken for a packet of data to be sent from one application, travel to, and be received by another application. This includes transit time over the network, and processing time at the source and the destination computers. Specifically, this is the time for encoding the packet for transmission and transmitting it, the time for that serial data to traverse the network equipment between the nodes, and the time to get the data off the circuit. This is also known as one-way latency. A minimum bound on latency is determined by the distance between communicating devices and the speed at which the signal propagates in the circuits. This is typically 70-95% of the speed of light. Actual latency is usually much higher. This is due to packet processing in networking equipment, and other traffic.
While every packet experiences some amount of lag, the term lag is typically used to refer to delays that are noticeable to a user. Latency is directly related to the physical distance that data travels. Thus, for example, the time taken for a packet to travel from a computer server in Europe to a client in the same region is likely to be shorter than the time to travel from Europe to the Americas or Asia. Protocols and well written code that avoid unnecessary data transmissions are less affected by the latency inherent in a network. Modern corporate networks have devices to cache frequently requested data and accelerate protocols. This reduces application response time, the cumulative effect of latency.
In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a host's hardware address when only its network layer address is known. ARP is not an IP-only or Ethernet-only protocol. Rather, ARP can be used to resolve many different network-layer protocol addresses to hardware addresses. However, due to the overwhelming prevalence of IPv4 and Ethernet, ARP is often used to translate IP addresses to Ethernet MAC addresses.
ARP is also used for IP over other LAN technologies, such as Token Ring, FDDI, or IEEE 802.11, and for IP over ATM. ARP is used in four cases of two hosts communicating. These include 1) when two hosts are on the same network and one desires to send a packet to the other; 2) when two hosts are on different networks and must use a gateway/router to reach the other host; 3) when a router needs to forward a packet for one host through another router; and 4) when a router needs to forward a packet from one host to the destination host on the same network.
The first case is used when two hosts are on the same physical network, i.e. capable of directly communicating without the use of a router. The last three cases are the ones more often used over the Internet. This is true because two computers connected to the Internet are typically separated by a communications path consisting of more than three hops.
When one host wants to send data to another, the sending host needs a destination IP address for the receiving host. This is the network layer address. The IP address is found in the DNS server for a particular URL. The sending host also needs a layer 2 destination address for the receiving host. This is a destination MAC address for the receiving host. When a router lies between the sending host and the receiving host, the router interface MAC address is used instead of the receiving host MAC address. ARP is implemented to satisfy these requirements.
The foregoing objects and advantages of the invention are illustrative of those that can be achieved by the various exemplary embodiments and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus, these and other objects and advantages of the various exemplary embodiments will be apparent from the description herein or can be learned from practicing the various exemplary embodiments, both as embodied herein or as modified in view of any variation which may be apparent to those skilled in the art. Accordingly, the present invention resides in the novel methods, arrangements, combinations and improvements herein shown and described in various exemplary embodiments.